check valve on cooling system

You should clamp your garden hose to the engine side of the strainer basket cooling hose when running up out of the water. When the engine turns on the water pump pulls water into the engine right away so there is no need to store water in the engine during shut down.

Wonder why it would start flowing back thru the pickup? Better question might be why didn't it before? I had a leak on my transmission cooler so I removed it and fixed the leak and then hooked everything back up. That is when it started flowing back to the pickup instead of overflowing out of the strainer. Weird. So now I am worried that sticking a garden hose into the strainer will not provide enough volume to cool engine in backyard.

1985 ski nautique 2001. Is there a check valve on the cooling system? The reason I ask is that for my "fake a lake" I have always stuck a garden hose into my strainer basket and this has worked fine for years. It has always overflowed into bilge until start-up and then it would suck down a little. Now it runs out of the water pickup on the bottom of the boat. It would make sense to have a check valve to "hold" the cooling water in the system during an engine shut off. But I can't find any reference of a check valve in the forums.
Does anyone know if there is a check valve between the pickup and the strainer basket?